Process for production of aromatic hydrocarbons



June 4, 1968 G. E. ADDISON 3,387,052

PROCESS FOR PRODUCTION OF AROMATIC HYDROCARBONS Filed May ll, 1966 2Sheets-Sheet 1 -I b t INVENTOR" a George E. Addison l: b a

.ATTOR/VEYS G. E. ADDISON 3,387,052

PROCESS FOR PRODUCTION OF AROMATIC HYDROCARBONS June 4, 1968 2Sheets-Sheet Filed May 11, 1966 mm M m R m E on m M M m a V E T N a m gr R m A 0 8 mm H K F R 8 mm mm \w mm /|M.N \m m Q f v t E v vw/ Q .r. mt I H 4! I 6 x m N 9 w t 9 k 1 W 0| m /|m S N Sas United States Patent-Oifice 3,387,052 Patented June 4, 1968 3,387,052 PROCESS FOR PRODUCTIONF ARGMATIC HYDROCARBUNS George E. Addison, Mount Prospect, Ill, assignorto Universal 0i! Products Company, Des Plaines, ill. a corporation ofDelaware Fiied May 11, 1966, Ser. No. 549,288 8 Claims. (Cl. 260-668)ABSTRACT OF THE DISCLOSURE Process which comprises charging naphtha to acatalytic reforming unit to produce aromatics and hydrogen, recoveringhigh purity aromatics from the resulting reformate, fractionating theresulting ramnate to provide a selected paraffinic fraction, andrecycling the selected parafiinic fraction to the reformer fordehydrocyclization to provide additional aromatics. The selectedparaffinic fraction is comprised of 0 hydrocarbons and has substantialfreedom from polycyclic aromatics. Where the catalytic reformercomprises a series of reaction zones, the selected paraffinic fractionis preferably recycled only to the last reaction zone.

The present invention relates to the production of aromatic hydrocarbonsfrom a selected petroleum fraction. More specifically, the presentinvention relates to a combination process for reforming a gasolineboiling range hydrocarbon wherein the production of aromatichydrocarbons is enhanced While substantially reducing the production ofparaflinic hydrocarbons.

In view of the profitability advantage in expanding into petrochemicals,the hydrocarbon processing industry has seen a world-wide trend awayfrom emphasis upon the production of high octane gasoline by catalyticreforming, and a shift toward maximization of aromatics production. Themaximization of aromatics has best been achieved commercially by thecombination of catalytic reforming and solvent extraction wherein highpurity aromatic hydrocarbons are produced and parafiinic rafiinate isrecovered. The paraffinic raffinate normally finds utility as a solvent,or a blending component for jet fuel, or a gasoline blending component.The parafiinic rafiinate is not a generally desired refinery product,however, since the market for parafifinic solvent is limited and therelatively low boiling range of some paraifinic fractions will oftenlimit their marketability as jet fuel components, it becomes necessaryin many instances to blend the parafiinic raffinate into the gasolinepool. Since the octane rating of parafiinic components is relativelylow, the refinery units which produce motor fuel must operate at moresevere conditions in order to provide high octane gasoline componentswhich will blend with low octane paraffinic components to provide thespecification octane rating on the final gasoline blend. Catalyst lifeand product yields are reduced by increased severity on the catalyticunits which produce high octane gasoline, and it is therefore apparentthat paraifinic raffinate is an undesirable refinery product where noexternal market exists for it as-produced.

As used herein, the term raffinate refers to the hydrocarbon product, orany fraction thereof, which remains after the aromatic content of theoriginal reformate product has been substantially removed by solventextraction or other processing means.

In the present invention, paraffini raffinate production is reduced byrecycling to the catalytic reformer. Similar combination processing hasbeen undertaken in the petroleum industry, but whereas such processinghas been technically feasible, it has not been commercially successful.Experience has shown that Where a paraifinic raflinate is recycled tothe catalytic reformer, the recycle stream accumulates in volumerequiring that at least a portion of such stream be removed in order tomaintain a constant hydrocarbon inventory within the combinationprocess. It has further been found that such combination processesrequire high operating severities which lead to increased rates ofcatalyst deactivation. In an eifort to overcome these handicaps, thefurther reforming of the paraflinic rafiinate stream has been attemptedin separate reforming facilities external to the first reformer zonewhich operates upon the fresh charge. Such double reformer systems havenot proven effective since in addition to the disadvantage of addedcapital and operating expense, such systems have not successfullyovercome the technical handicaps noted herein.

It is therefore an objective of the present invention to enhance theproduction of aromatic hydrocarbons while minimizing the production ofparaffinic raffinate. It is a further objective of the present inventionto afford a means whereby the distribution between aromatic product andparafiinic product may be varied as required to supply the needs of afluctuating market. It is a more specific objective of the presentinvention to afford a means whereby these ends are achieved whileproviding substantially improved catalyst life at a reduced capital andoperating expense.

Therefore, in accordance with the practice of this invention, oneembodiment thereof comprises contacting hydrocarbon feed stockcontaining naphthenic and paraffinic compounds with hydrogen in areaction zone under conditions suitable to convert at least a portion ofsaid naphthenes into aromatic compounds; separating the eflluent fromsaid reaction zone into a hydrogen-rich product and a product containingsaid aromatic compounds; subjecting said aromatic-containing product toconditions suificient to produce a first paraflinic product and aproduct comprising monocyclic aromatics; recovering said monocyclicaromatic product; subjecting said first parafiinic product to conditionssufficient to produce at least an intermediate paraffinic productcomprising hydrocarbons having at least eight carbon atoms per moleculeand having substantial freedom from polycyclic aromatics; and recyclingat least a portion of said intermediate paraffinic product to thereaction zone.

A modified embodiment of the present invention, comprises contacting ahydrocarbon feed stock containing naphthenic and parafiinic compoundswith hydrogen in a reaction Zone under conditions suitable to convert atleast a portion of said naphthenes into aromatic compounds; separatingthe efiluent therefrom into at least a hydrogen rich gas product and aproduct containing said aromatic compounds; subjecting saidaromatic-containing product to conditions suificient to provide at leasta light aromatic-containing fraction comprised of hydrocarbonscontaining from about six to about eight carbon atoms per molecule and aheavy aromatic-containing fraction comprised of hydrocarbons containingabout nine or more carbon atoms per molecule; separating said lightaromatic-containing fraction into a first parafiinic fraction and alight aromatic product; separating said heavy aromatic-containingfraction into a second paratiinic fraction and a heavy aromatic product;recovering said light aromatic product and said heavy aromatic product;subjecting said first paraffinic fraction and said second paraflinicfraction to conditions sufficient to provide at least an intermediateparafrinic product comprising hydrocarbons having at least eight carbonatoms per molecule, and having substantial freedom from polycyclicaromatics; and returning at least a portion of said intermediateparaffiuic product to the reaction zone wherein at least a portion ofsaid product is converted to aromatic compounds.

In the most specific embodiments of the present invention, the desiredends are achieved wherein the reaction zone is comprised of multiplestage contact sections and the portion of said intermediate paraflinicproduct which is recycled is returned only to the last of said multiplestage contact sections.

The foregoing embodiments are illustrated by FIG- URE I and FIGURE 11which are schematic flow diagrams of the inventive process. FIGURE I isillustrative of the present invention in its broad embodiment whileFIGURE II comprises a more specific application of the presentinvention.

The charge stocks which may be reformed in accordance with the presentinvention comprise gasoline boiling range hydrocarbons containingnaphthenes, paraffins, and aromatics with only minor amounts of olefinsbeing present. Suitable hydrocarbon charge may be a straight rungasoline or a natural gasoline, or it may be a refined gasoline such asa thermal cracked gasoline or a hydrocracked gasoline, etc, or it maycomprise any combination thereof. The gasoline may be a full boilingrange gasoline fraction having an initial boiling point of from about 50F. to about 100 F. and an end boiling point of from about 375 F. toabout 425 F, or it may be a selected fraction thereof. The usualfraction to be processed in the present invention will be a selectednaphtha fraction having an initial boiling point of from about 150 F. toabout 250 F. and an end boiling point of from about 350 F. to about 425F. Where such fraction comprises substantial sulfur ornitrogen-containing hydrocarbons, or where substantial olefinichydrocarbons are included, hydrogen pretreatment may be necessary inorder to profeet the reforming catalyst from loss of activity.

Hydrogen pretreatment of contaminated hydrocarbon charge stocks is wellknown in the art of hydrocarbon processing, and a typical method isshown in U.S. Letters Patent No. 2,878,180. Any hydrocarbon charge stockcontaining more than about 10.0 parts per million (p.p.m.) by weight ofsulfur and/or more than about 1.0 ppm. of nitrogen and/or more thanabout 1.0 volume percent of olefinic hydrocarbons should be treated.Hydrogen pretreatment will also serve to remove trace quantities ofarsenic, lead, copper, nickel, vanadium, tungsten, and other metalswhich may be present in untreated hydrocarbon fractions and which may bedetrimental to noble metal reforming catalysts.

The basic processing techniques of catalytic reforming and a preferredcatalyst are indicated in U.S. Patents No. 2,479,109 and 2,479,110wherein the catalyst comprises alumina, platinum and halogen. Reformingis accomplished at a temperature in the range of from about 600 F. to1100 F; at a pressure in the range of from about 100 p.s.i.g. to 1000p.s.i.g.; at a liquid hourly space velocity in the range of from about0.5 to 10.0; and in the presence of from about 0.5 to 10.0 moles ofhydrogen per mole of hydrocarbon. The hydrogen is normally present asthe major component of a hydrocarbon-containing gas which is circulatedwith the charge stock at a rate of from about 500 to 13,000 standardcubic feet of gas per barrel of liquid charge stock.

As understanding of the reaction mechanisms occurring within thereforming zone has increased, it has become possible to adjust operatingtechniques and to modify catalyst composition in order to enhance thespecific reaction desired. It has been determined that catalyticreforming is characterized by four specific chemical reactions: (1) thedehydrogenation of naphthenic hydrocarbons to produce the correspondingaromatic derivative; (2) the dehydrocyclization of parafiinichydrocarbons to produce corresponding aromatic hydrocarbons; (3) thehydrocracking of high molecular weight hydrocarbons; and (4) theisomerization of normal parafiinic hydrocarbons to produce branchedchain isomers of equal molecular weight. Each of these four reactionmechanisms upgrade low octane hydrocarbons to high octane hydrocarbons,but as the automotive manufacturers have increased engine compressionratios, it has become necessary to adjust operating techniques in orderto control the reaction mechanisms selectively to maximize octane withminimum loss of liquid product yield. It has been determined that thedehydrogenation of naphthenes to aromatics is promoted by operating atlower pressure levels; that dehydrocyclization of paraffins to aromaticsis promoted by low pressure and high temperature; that hydrocracking ofparaffins is promoted by high pressure, high temperature, and highresidence time of the charge stock on the catalyst; and thatisomerization of parafiins is promoted by intermediate temperature and acatalyst containing a much higher halogen content than normallyemployed. The reforming catalyst is, therefore, composited in a mannerto effect the desired balance between the competing reactions, and apreferred catalyst is comprised of 0.375 wt. percent platinum, 0.350 wt.percent fluorine, 0.900 -wt. percent chlorine, and 98.375 wt. percentalumina.

The catalytic reforming unit of the present invention is maintained atoperating conditions to enhance the dehydrogenation of naphthenes andthe dehydrocyclization of paraffins in order to maximize the productionof both aromatics and hydrogen, maximum hydrogen production also beingdesired since it is consumed elsewhere in many petroleum refinery andpetrochemical complexes. The production of aromatic hydrocarbons isenhanced by catalytic reforming at a temperature in the range of fromabout 850 F. to 1050" F., and at a pressure in the range of from about100 p.s.i.g. to 400 p.s.i.g. when the end boiling point of the chargestock is about 350 F. However, when the end point of the charge stock isabout 400 F. or more, the preferred pressure is about 500 p.s.i.g. inorder to maintain catalyst stability. Charge stocks having end points ofabout 400 F. comprise higher molecular weight hydrocarbons which have agreater tendency to hydrocrack. The hydrocracking mechanism formscarbonium ions, olefinic fragments, and carbon. The olefinic fragmentsbecome saturated with hydrogen in-part, but some of the fragments willpolymerize with carbonium ions to form polycyclic aromatics. The carbonproduced is retained upon the catalyst surface and some of thepolycyclic aromatics are so retained, thus detrimentally effectingcatalyst activity and selectivity. The processing of such highermolecular weight charge stocks at 500 p.s.i.g. gives a higher partialpressure of hydrogen which is to be preferred since it retards carbonformation and enhances saturation of the olefinic fragments thusretarding the formation of polycyclic aromatics.

The aromatics separation Zone of the present invention may becharacterized by a solvent extraction technique, or an aromatics solidadsorption technique, or an extractive distillation technique, or afractional crystallization technique. A preferred separation method isdescribed by US. Patent No. 2,730,558. A particularly preferred solventfor separating aromatic hydrocarbons from non-aromatic hydrocarbons is amixture of water and one or more hydrophilic organic solvents. Such acombination solvent may have its solubility regulated by varying thewater content. Thus, by adding more water to the solvent, the solubilityof all components in the hydrocarbon mixture is reduced, but thesolubility difference between components (selectivity) is increased. Thenet effect is to decrease the number of contacting stages required toachieve a given purity of product, or to increase the resulting purityof product where the number of contacting stages is held constant.Because of the resulting reduction in solubility due to the increasedwater content, the throughput of the combination solvent must beincreased in order to dissolve the solute at the same production rate.Suitable hydrophilic organic solvents for this process include alcohols,glycols, aldehydes, glycerine, phenol, etc. Particularly preferredsolvents are diethylene glycol, triethylene glycol, dipropylene glycol,tripropylene glycol, and mixtures thereof containing from about 2% toweight of water. In classifying hydrocarbon and hydrocarbon-typecompounds according to increasing solubility in such mixed solvent, itis found that paraflins are least soluble, followed in increasing orderof solubility by naphthenes, olefins, diolefins, acetylenes,sulfurcontaining hydrocarbons, nitrogen-containing hydrocarbons, andaromatic hydrocarbons. It may thus be seen that the ideal charge to sucha solvent extraction process is one consisting essentially of paraflinsand aromatics, and that since catalytic reformates contain only minoramounts of naphthenes and olefins, reformates are well suited to such anaromatics extraction procedure.

Aromatic hydrocarbons differ in their relative solubility in the solventin that solubility is a function of normal boiling point, with thelighter aromatics being more soluble than the heavier aromatics.Similarly, the solubility of non-aromatic hydrocarbons also decreaseswith increasing normal boiling point. Thus, in operation of a singleextraction system upon a full boiling range catalytic reformate, the lowmolecular weight aromatics may be extracted to recover high puritybenzene, toluene, ethylbenzene, and xylenes, with little or nocontamination by naphthenes and paraffins, but the paraffin-richrafiinate will contain substantial heavy alkylaromatics and polycyclicaromatics. However, if the extraction conditions are modified to recovernot only the light aromatics but the heavy aromatics as well,substantial contamination by non-aromatics will occur in the aromaticproduct. The lower molecular weight paraffins have solubilitiescomparable to the higher molecular Weight aromatics and these paraflinsare indiscriminately dissolved in the selective solvent. The maximumeffective recovery of pure aromatics and paraffin-rich raffinate istherefore not technically feasible without a double extraction system.In such a system, the aromatic-containing hydrocarbon feed isfractionated to provide a light fraction and a heavy fraction. The lightfraction, comprised of aromatics containing from six to eight carbonatoms per molecule, is charged to one extraction system and the heavyfraction, comprised of aromatics containing about eight or more carbonatoms per molecule, is charged to a second extraction system. Since thelight paraffins are concentrated in the light fraction, recovery of theheavy aromatics in the second extraction system is accomplished withoutsolubility interference from such paraflins.

The split betwen the light and heavy fractions will vary in accordancewith the concentration and composition of the aromatics contained withinthe hydrocarbon feed. In some instances the first extraction system willrecover benzene and toluene, while the second extraction system willrecover the heavier aromatics. In other cases the first extractionsystem will recover benzene, toluene, ethylbenzene, and xylenes, whilethe second extraction system may recover aromatics containing nine ormore carbon atoms per molecule. It is readily apparent that such adouble extraction system will entail increased capital and operatingexpense. Because of the economic considerations involved, it istherefore customary to extract maximum benzene, toluene, ethylbenzenes,and xylenes in a single extraction system and allow substantial amountsof the heavier aromatics to remain in the paraflinic rafinate.

In the present invention, the paraffin-rich rafiinate is distilled in afractionation zone to provide a selected par atlinic raffinate streamwhich is recycled to the catalytic reformer.

The total paraffin-rich ralfinate is first fractionated to remove allhex'anes and heptanes which are recovered as a by-product stream.Although hexanes and heptanes may be isomerized and dehydrocyclicized inthe catalytic reforming zone, it has been determined that these lightparaflins are not effectively reformed in the presence of highermolecular Weight paraffins. The primary reason for this is that thereforming catalyst will selectively dehydrocy-clicize the heavierparafiins at less severe operating conditions, and operating severitiesrequired to dehydrocyclicize hexanes and heptanes cannot be approachedwithout resulting in 'an excessive yield loss due to undesiredhydrocracking of other hydrocarbons. In addition, the octanes andheavier parafiins are not only dehydrocyclicized to form aromatics, butthey are also hydrocracked to form lighter paraflins, including hexanesand heptanes. Thus, it has been found that the net result of recycling araffinate comprising hexane and heavier parafiins is that the recyclestream accumulates hexanes and heptanes and provision must, therefore,be made for removing this accumulation. This may be accomplished bydrawing off a portion of the recycle stream, but since such a dragstream would also remove octane and heavier hydrocarbons, the preferredmethod is to continually remove hexanes and heptanes by fractionation.

The resulting deheptanized paraffinic rafiinate stream must be furtherfractionated to remove all polycyclic aromatics. The polycyclicaromatics may be removed in the aromatics separation zone by adjustmentof the solvent composition, use of a high solvent circulation rate, andprovision of a greater number of contact stages, but such changes inoperation cannot produce a completely aromatic-free rafiinate and acompletely parafiin-free aromatic product without entailing prohibitivecapital and operating expenses. Since polycyclic aromatics have higherboiling points than the paraffins having an equal number of carbonatoms, the most economical and the preferred method of removingpolycyclic aromatics from the deheptanized parafiinic rafiinate is byremoving them as a bottoms product in the rafiinate fractionation zone.The polycyclic aromatics must be removed from the raffinate beingrecycled to the reformer since failure to remove the polycyclicaromatics will cause them to accumulate in the recycle stream. It mustalso be noted that such an accumulation of polycyclic aromatics has beenfound to be a primary cause of acceleration in the rate of loss ofreforming catalyst activity. Certain species of such hydrocarbons tendto be retained on the cat 'alyst surface without being effectivelyreacted in any manner and the catalytically active sites becomeeffectively shielded from the material being processed. The net resultis that catalyst activity and selectivity are prematurely destroyed. Itis, therefore, the practice of the present invention to remove thepolycyclic aromatics from the paraffinic rafiinate by fractionating theraffinate to an end boiling point of about 350 F. or less.

The resulting paraffinic fraction, comprising octanes and heavierhydrocarbons and being substantially free of polycyclic aromatics, isrecycled to the catalytic reforming zone as the selected paraffinicraffinate stream. By specific exclusion of hexanes, heptanes,andpolycyclic aromatics from the recycle rafiinate stream, the

problems noted above which have been experienced in similar combinationprocessing are eliminated.

The dehydrogenation of the naphthenic hydrocarbons of the fresh chargestock to form aromatic hydrocarbons in the catalytic reforming zone is ahighly endothermic reaction, and the hydrocarbon and hydrogen mixedstream must be intermittently reheated in order to maintain the mixtureat effective reaction temperatures. The catalytic reforming zone is,therefore, comprised of several reactor vessels containing the reformingcatalyst and reheating is provided between reactors. Since the amount ofendothermic reaction will vary in accordance with the concentration ofnaphthenes in the hydrocarbon charge stream, the number of reheatingapplications will vary. Thus, it is normal for 'a catalytic reformer tobe provided with three reactors and two interheaters, but where thenaphthene content of the charge stock is in excess of 45 volume percent,at least three reheatings are normally required to maintain adequatetemperature on the catalyst and thus at least four reactors must beprovided.

In a more specific embodiment of the present invention, the selectedparaflinic raffinate may be sent only to the last of the severalreactors whenever the naphthene content of the paraffinic raffinate islow. Since substantial naphthene dehydrogenation occurs in the precedingreactors, the endothermicity causes the average catalyst temperature inthese vessels to be substantially below what is required for effectivedehydrocyclization of the predominantly paraffinic recycle refiinate.The amount of dehydrocyclization which may occur in the precedingreactors may be accomplished upon the parafiinic hydrocarbons which areintroduced into the catalytic reformer by the fresh charge stock and thepresence of additional parafiins from the selected parafiinic rafiinateis unnecessary and may be, in fact, undesirable. The naphthene andparaffins have comparable adsorption rates upon the catalyst and it isadvantageous to minimize the competition between these hydrocarbon typesfor the active catalyst sites. The dehydrogenation of naphthenes to formaromatics is the selective reaction which is promoted by the catalystand it is a relatively clean reaction, whereas the dehydrocyclization ofparafiins is not as clean in that it is accompanied by hydrocrackingwith the resulting deposition of carbon upon the catalyst. Thus,catalyst activity may be detrimentally effected by combining theselected paraffinic rafiinate with the fresh charge stock and passing itthrough all reactors when the naphthene content of the selectedraffinate stream is less than 10.0 volume percent.

In addition, it must be noted that the selected parafiinic raffinatestream will contain olefinic hydrocarbons and that their concentrationmay be substantial in a high severity reforming operation. Since olefinsare more easily adsorbed upon the catalyst surface than eithernaphthenes or paraffins, the balance of catalyst selectivity betweencompeting reaction mechanisms may be detrimentally upset by excessiveolefins. Thus, by introducing the raffinate into the entire series ofreactors, the dehydrogenation of naphthenes to form aromatics will beretarded, and excessive naphthene dehydrogenation reaction will beshifted into the last reactor of the series. Further, the olefins areknown to polymerize to produce higher molecular weight parafiins, alkylaromatics, and polycyclic aromatics. Certain of these polymerizationproducts and more specifically certain polycyclic aromatics, are knownto be adsorbed upon the catalyst surface where they effectively mask theactive sites. Such polymerization will occur to some extent in allreactors since olefins as well as carbonium ions are produced asintermediate reactants in the reforming reactions, but normally thispolymerization is concentrated in the last reactor where the temperatureis more severe. Thus, introduction of excessive olefins into the firstreactors of the series will cause accelerated catalyst degradation andsuch result is minimized by intro ducing the selected parafiinicraffinate only to the last reactor where polymerization products have agreater chance of being hydrocracked due to the higher temperature levelwhich is maintained.

Therefore, in the practice of the present invention it is a preferredembodiment to recycle the selected paraffinic rafiinate only to the lastof the several reforming reactors whenever the selected paraffinicrafiinate contains less than 10 volume percent of naphthenes, or when itcontains more than 1.0 volume percent of olefins.

The process of the present invention may be more clearly understood byreference to the accompanying drawings which illustrate the variousembodiments thereof.

Referring now to FIGURE 1, a charge stock comprising parafiinic andnaphthenic hydrocarbons enters the process of the present invention vialine 1 whereby it enters a catalytic reforming zone at a pressure in therange of from about p.s.i.g. to 500 p.s.i.g. The charge stock is admixedwith a hydrogen-containing gas which enters line 1 by means of line 18.In addition, a selected paraffinic raffinate stream may enter line 1 bymeans of line 30 as will be further noted hereinbelow, but in theinstant embodiment, line 30 is isolated by appropriate valving and nohydrocarbon stream is thereby introduced into line 1. The resultingmixture of charge stock and hydrogen-containing gas passes by means ofline 1 into heater 2 wherein its temperature is raised to a level in therange of from about 850 F. to 1050" F. The heated mixture leaves vialine 3 and enters a first catalytic reforming reactor 4 containing asuitable catalyst comprising aluminum, platinum, and chlorine wherein asubstantially endothermic catalytic reaction occurs due to thedehydrogenation of naphthenes to form aromatic hydrocarbons andhydrogen. The resulting mixture passes via line 5 into heater 6 whereinthe temperature of the stream is again raised to a level in the range offrom about 850 F. to 1050 F. Leaving by means of line 7, the streamenters a second reforming reactor 8 wherein a further endothermiccatalytic reaction occurs due to the further dehydrogenation ofnaphthenes. The resulting stream leaves via line 9 wherein it is mixedwith the selected parafiinic raffinate stream which enters via line 31and which is to be specified hereinbelow. The mixed stream then entersheater 10 wherein the temperature is again raised to a level in therange of from about 850 F. to 1050 F. The heated mixture leaves via line11 and enters a third reforming reactor 12 wherein substantial catalytichydrocrackin-g and dehydrocyclization of parafiins occurs. The finaleffluent leaves via line 13 and upon cooling enters a phase separator14, wherein a hydrogencontaining gas phase and a liquid hydrocarbonphase are separated. The hydrogen-containing gas phase is Withdrawn vialine 15 and the net hydrogen-containing gas which is generated withinthe catalytic reforming zone is withdrawn therefrom via line 16 as aproduct stream. The balance of the hydrogen-containing gas passes vialine 15 to a recycle compressor 17 by means of which the gas iscompressed. The compressed gas is discharged from compressor 17 via line18 and enter line .1 wherein it is admixed with the hydrocarbon chargestock as previously noted.

A11 unstabilized hydrocarbon product, comprising substantial aromatics,leaves phase separator 14 via line 19 and passes into a firstfractionation zone 20 which may be comprised of one or morefractionating columns as required to effect the desired separations. Theunstabilized hydrocarbon product is fractionated to remove dissolvedgases and light non-aromatic hydrocarbons. A gaseous product comprisinghydrogen, methane, ethane and propane leaves fractionation zone 20 vialine 21 while a first light non-aromatic hydrocarbon product comprisingbutanes and pentanes is withdrawn by means of line 22. An aromatic-richstream comprising hexane and heavier hydrocarbons is withdrawn via line23 and passed into an aromatics separation zone 24 which preferably iscomprised of a solvent extraction process as previously noted. The highpurity aromatic product stream is withdrawn via line and it may be sentto subsequent distillation means for fractionation into its separatearomatic components.

A paraflinic rafiinate stream, containing heavy alkylaromatics andpolycyclic aromatics, leaves the aromatic separation zone 24 by means ofline 26 and enters a raffinate fractionation zone 27. This fractionationzone 27 will be comprised of one or more fractionating columns as may berequired to effect the distillation of the raftinate to remove hexanesandheptanes and to remove polycyclic aromatics. A second lighthydrocarbon product stream comprising hexanes and heptanes is withdrawnfrom fractionation zone 27 by means of line 28. This paraflinic productstream will also contain traces of benzene and toluene as well asamounts of olefins and naphthenes which contain from six to about sevencarbon atoms per molecule. A heavy hydrocarbon product stream,containing heavy alkylaromatics and polycyclic aromatics as well .asheavy paraffins, is Withdrawn via line 29.

The selected parafiinic rafiinate stream, comprised of paraifins havingeight or more carbon atoms per molecule and having substantial freedomfrom polycyclic aromatics, is withdrawn from fractionation zone 27 vialine 30. This selected paraifinic rafiinate stream may be introducedinto line 1 by means of line as previously noted hereinabove. Since thisstream is principally comprised of parafiins and since it contains someolefins, for reasons previously discussed, the preferred embodiment ofthe inventive process is not to return this stream to line 1. Thepreferred embodiment is to isolate line 30 from line 1 with appropriatevalving, and withdraw this paraifinic raffinate stream from line 30 bymeans of line 31. The selected paraffinic rafiinate stream passesthrough line 31 and is injected into line 9 as the stream specifiedhereinabove, wherein it is mixed with the effluent leaving reactor 8.The mixed stream enters reactor 12 by means previously noted and theparaifinic hydrocarbons which have been recycled from the raffinatefractionation zone 27 are catalytically dehydrocyclized in reactor 12 toproduce additional aromatic hydrocarbons.

Where the hydrocarbon charge stock of the inventive process has a highend boiling point, say from about 375 F. to 425 F., a considerablevolume of aromatics will be produced having nine or more carbon atomsper molecule. For reasons previously set forth, such aromatics cannot beeffectively recovered without a double aromatics extraction system. Sucha processing combination as applied to the present invention isillustrated by the diagram of FIGURE 2.

Referring to FIGURE 2, a charge stock comprising paraffinic andnaphthenic hydrocarbons enters the inventive process via line 1 wherebyit enters a catalytic reforming zone at a pressure in the range of fromabout 160 p.s.i.g. to 500 p.s.i.g. The charge stock is admixed with ahydrogen-containing gas which enters line l by means of line 18. Inaddition, a selected paraifinic raffinate stream may enter line 1 bymeans of line 31 as will be further noted hereinbelow, but in theinstant embodiment line 31 is isolated with appropriate valving and nohydrocarbon stream is thereby introduced into line 1. The resultingmixture of charge stock and hydrogen-containing gas passe by means ofline 1 into heater 2 wherein its temperature is raised to a level in therange of from about 850 F. to 1050 F. The heated mixture leaves via line3 and enters a first catalytic reforming reactor 4 containing a suitablecatalyst wherein a substantially endothermic catalytic reaction occursdue to the dehydrogenation of naphthenes to form aromatic hydrocarbonsand hydrogen. The resulting mixture passes via line 5 into heater 6wherein the temperature of the stream is again raised to a level in therange of from about 850 F. to 1050" F. Leaving by means of line 7, thestream enters a second reforming reactor 8 wherein a further endothermiccatalytic reaction occurs due to the further dehydrogenation ofnaphthcnes. The resulting stream leaves via line 9 wherein it is mixedwith the selected parafiinic raifinate stream which enters via line 32and which is to be specified hereinbelow. The mixed stream then entersheater 10 wherein the temperature is again raised to a level in therange of from about 850 F. to 1050 F. The heated mixture leaves via line11 and enters a third reforming reactor 12 wherein substantial catalytichydrocracking and dehydrocyclization of parafiins occurs. The finalefiluent leaves via line 13, and upon cooling, enters a phase separator14, wherein a hydrogen-containing gaseous-vapor phase and a liquidhydrocarbon phase are separated. The hydrogen-containing gaseous-vaporphase is withdrawn via line 15 and the net hydrogen-containing gas whichis generated within the catalytic reforming zone is withdrawn therefromvia line 16 as a product stream. The balance of the hydrogen-containinggas passes via line 15 to a recycle compressor 17 by means of which thegas is compressed. The compressed gas is discharged from compressor 17via line 18 and enters line 1 wherein it is admixed with the hydrocarboncharge stock as previously noted.

An unstabilized hydrocarbon product, comprising substantial aromatics,leaves phase separator 14 via line 19 and passes into a firstfractionation zone 29 which may be comprised of one or morefractionating columns as required to effect the desired separations. Theunstabilizcd hydrocarbon product is fractionated to remove dissolvedgases and light non-aromatic hydrocarbons. A gaseous product comprisinghdrogen, methane, ethane, and propane leaves fractionation zone 20 vialine 21 while a first light non-aromatic hydrocarbon product comprisingbutanes and pentanes is withdrawn by means of line 22. A firstaromatic-containing stream comprised of hydrocarbons having from sixto-abc-ut eight carbon atoms per molecule is withdrawn via line 24 andpassed into a first aromatics separation zone 25. A secondaromatic-containing stream comprised of hydrocarbons having about nineor more carbon atoms per molecule is withdrawn via line 23 and passedinto a second aromatics separation zone 33. Both aromatics separationzones may be characterized by the solvent extraction processing methodpreviously set forth.

A product stream of high purity light aromatics containing benzene,toluene, ethylbenzene, and xylenes is removed from aromatics separationzone 25 by means of line 26, and a product stream of high purity heavyaromatics containing about nine or more carbon atoms per molecule isremoved from aromatics separation zone 33 by means of line 34. Thesearomatic product streams may be sent to subsequent distillation meansfor fractionation into the separate aromatic product components.

A light parafiinic raffinate stream comprising hydrocarbons having fromsix to about eight carbon atoms per molecule leaves the first aromaticsseparation zone 25 via line 27 and is mixed with a heavy parafiinicratfinate stream comprising hydrocarbons having about nine or morecarbon atoms per molecule which leaves the second aromatics separationzone 33 via line 35. The two mixed rafiinate streams pass via line 27and enter a raflinate fractionation zone 28. This fractionation zone 28will be com prised of one or more fractionating columns as may berequired to effect the distillation of the raflinate to remove hexanesand heptanes and to remove polycyclic aromatics. A second lighthydrocarbon product stream comprising hexanes and heptanes is withdrawnfrom fractionation zone 28 by means of lines 29. This parafrinic productstream will also contain traces of benzene and toluene as well asamounts of olefins and naphthenes which contain from six to about sevencarbon atoms per molecule. A heavy hydrocarbon product stream,containing heavy alkylaromatics and polycyclic aromatics, as well asheavy paraffins. is withdrawn via line 30.

The selected paraffinic raffinate stream, comprised of parafrins havingeight or more carbon atoms per molecule and having substantial freedomfrom polycyclic aromatics, is withdrawn from fractionation zone 28 vialine 31. This selected paraifinic raffinate stream may be introducedinto line 1 by means of line 31 as previously noted hereinabove. Sincethis stream is principally comprised of paraffins, and since it containssome olefins, for reasons previously discussed, the preferred embodimentof the inventive process is not to return this stream to line 1. Thepreferred embodiment is to isolate line 31 from line 1 with appropriatevalving, and withdraw this paraffinic raffinate stream from line 31 bymeans of line 32. The selected paraffinic rafiinate stream passesthrough line 32 and is injected into line 9 as the stream specifiedhereinabove, wherein it is mixed with the efiluent leaving reactor 8.The mixed stream enters reactor 12 by means previously noted and theparaffinic hydrocarbons which have been recycled from the raflinatefractionation zone 28 are catalytically dehydrocyclicized in reactor 12to produce additional aromatic hydrocarbons.

In the foregoing generalized narrations of the inventive process, nooperating conditions have been indicated for the fractionation zones orthe aromatic separation zones. Such conditions will of necessity vary inaccordance with the composition of the hydrocarbon streams beingprocessed, as well as with the physical characteristics of theprocessing equipment utilized. Those skilled in the art will readilyascertain the operating conditions which may be required to effect thephysical separations of the hydrocarbon components therein,

The advantages of the inventive process will be most effectivelyillustrated by the following examples. Example 1 illustrates the yieldsof aromatic products and parafiinic raifinates which are obtained bycatalytic reforming of a specific hydrocarbon charge stock incombination with solvent extraction of the aromatics wherein no recycleof the paraiiinic ratiinate is practiced. Example 2 illustrates theyields of aromatic products and paraffinic rafiinate products which areobtained by catalytic reforming of the same hydrocarbon charge stock incombination with solvent extraction of the aromatics, wherein theselected parafiinic rafiinate is recycled to the catalytic reformer inaccordance with the practice of the present invention.

Example 1 A full boiling range naphtha having an initial boiling pointof 160 F. and an end boiling point of 375 F. is charged to a catalyticreformer at a liquid hourly space velocity of 1.4. The naphtha has agravity of 590 API and has a volumetric composition of 60 vol. percentparaffins, 30 vol. percent naphthenes, and vol. percent aromatics. Thecharge stock is processed with 7.5 moles of hydrogen per mole ofhydrocarbon at a pressure of 400 p.s.i.g. in the presence of a reformingcatalyst comprised of alumina, platinum, and chlorine. The catalyst isconained in three reactors with the first reactor containing of thecatalyst, the second reactor containing of the catalyst, and the thirdreactor containing of the catalyst. The naphtha is charged to theprocess at the rate of 12,000 barrels per stream day (b.p.s.d.) and isheated therein to provide that the mixed hydrocarbon and hydrogen streamenters each reactor at a temperature of 965 F. Upon cooling andseparation of the efiluent into a gas phase and a liquid phase, the gasphase is recirculated to the reactor section in accordance with the artof catalytic reformin and a portion of the gas phase is withdrawn as anet product. The unstabilized liquid phase is passed to a fractionationsection wherein an aromaticrich stream comprised of hydrocarbons havingsix or more carbon atoms per molecule is recovered at a rate of 8270b.p.s.d. This stream is charged to a solvent extraction system wherein4902 b.p.s.d. of high purity aromatic hydrocarbons are recovered forfurther processing, and 3368 b.p.s.d. of paratlinic raflinate arerecovered and sent to product storage. The aromatic product is passed toan aromatic fractionation system wherein it is separated to 12 providehigh purity aromatic component products comprising 420 b.p.s.d. ofbenzene, 1032 b.p.s.d. of toluene, 1638 b.p.s.d. of mixed ethylbenzeneand xylenes, and 1812 b.p.s.d. of aromatics containing nine or morecarbon atoms per molecule.

Example 2 The full boiling range naphtha defined in Example 1 is chargedto a catalytic reforming unit at a rate of 12,000 b.p.s.d. and a liquidhourly space velocity of 1.3 in the presence of 7.5 moles of hydrogenper mole of hydrocarbon at a pressure of 400 p.s.i.g. The reactorsection is composed of three reaction vessels containing a catalystcomprised of alumina, platinum and chlorine distributed in the reactorswith 20% of the catalyst contained in the first reactor, 30% in thesecond, and 50% in the third. A selected paratfinic rafiinate stream isintroduced into the reactor section at a rate of 1187 b.p.s.d and isprocessed through the third reactor only. The full boiling rangenaphtha, in conjunction with the selected paraffinic raffinate, amountsto a combined feed of 13,187 b.p.s.d. yielding an effective liquidhourly space velocity of 1.4. Sufficient heating means are provided toassure that the combined hydrogen and hydrocarbon stream entering eachreactor is introduced therein at a temperature of 965 F. The finalefiiuent leaving the third reactor is cooled and separated into a gasphase and a liquid phase. The gas phase is recirculated through thereaction vessels in accordance with the art of catalytic reforming and aportion of the gas is withdrawn as a net product.

The unstabilized liquid phase is passed to a fractionation sectionwherein an aromatic-rich stream comprised of hydrocarbons having six ormore carbon atoms per molecule is recovered at a rate of 8980 b.p.s.d.This stream is then passed to a solvent extraction system wherein 5456b.p.s.d. of high purity aromatic hydrocarbons are withdrawn, and 3524b.p.s.d. of paraifinic raffinate are withdrawn. The aromatic product ispassed to an aromatic fractionation system wherein it is separated toprovide high purity aromatic component products comprising 448 b.p.s.d.of benzene, 1108 b.p.s.d. of toluene, 2084 b.p.s.d. of ethylbenzene andmixed xylenes, and 1816 b.p.s.d. of aromatics containing nine or morecarbon atoms per molecule. The parafiinic raffinate stream is passed toa raffinate fractionation section wherein the rafiinate is separated toprovide 2156 b.p.s.d. of a light rafiinate product containinghydrocarbons having from six to seven carbon atoms per molecule, 181b.p.s.d. of a heavy ratfinate product containing about 53.0 vol. percentof polycyclic aromatics and heavy alkylbenzenes, and 1187 b.p.s.d. of aselected parafiinic raffinate stream comprised of hydrocarbons having atleast eight carbon atoms per molecule and having substantial freedomfrom polycyclic aromatics. The selected paraflinic rafiinate stream,having an initial boiling point of 225 F. and an end boiling point of320 F., ocntains 9.3 vol. percent naphthenes and 0.5 vol. percentolefins. This selected rafiinate stream is sent back to the catalyticreformer and introduced into the hydrogenhydrocarbon stream which feedsthe third reaction vessel as has been previously noted hereinbefore.

The foregoing Example 1 provides an indication of the yields of aromatichydrocarbons and of paraflinic rafiinate obtained when the subject fullboiling range naphtha is catalytically reformed followed by extractionof aromatics in accordance with the current processing art. Theforegoing Example 2 provides an indication of the yields of aromatichydrocarbons and of paraifinic rafiinate obtained when the subjectnaphtha is catalytically reformed and solvent extracted in accordancewith the present invention whereby the selected parafiinic raffinatefraction is recycled to the catalytic reforming zone. The advantage ofthe present invention is most readily ascertained by referring to TableA below wherein the results indicated in the examples are tabulated forease of comparison. For reliability of comparison, the solventextraction efi1- ciences' in recovering the individual aromaticcomponents were held the same in the two processing examples.

TABLE A.-PROCESSING 12,000 B.P.S.D. OF FULL BOILING RANGE NAPHTHAExample 1- Example 2- Reforming Reforming and and Extraction Extractionwithout with Raflinate Recycle Recycle Daily Production, b.p.s.d.Aromatic Products:

Benzene 420 448 Toluene l, 032 l, 108 Total C3 Aromat 1, 638 2, 084Aromatics 1, 812 1, 816

Total Aromatics 4, 902 5, 456

Parafiinic Rafl'mate Products: N Light Rafiinate .1 2, 156 HeavyRafimate... 181

Total Rafiinato 3, 368 2, 337

Product Yields, Volume Percent of Naphtha Feed Aromatics Yields:

Benzene 3. 50 3. 73 Toluene 8. 60 9. 23 Total 03 Aromatics 13. 65 17. 340 Aromatics 2 15.10 15.13

Total Aromatics 40. 85 45. 43

Parafiinic Raffinate Yields:

Light Raflinate 17. 96 Heavy Rafllnate 1. 50

Total Ratfinate 28. 07 19. 46

1 C is defined as having eight carbon atoms per molecule. 2 0 is definedas having nine or more carbon atoms per molecule.

It will be noted that the inventive process has the advantage ofincreasing aromatic hydrocarbon production and yields while decreasingthe production and yields of parafiinic rafiinate. As indicated in TableA above, the present invention resulted in an increase in the yield oftotal aromatics from 40.85 vol. percent to 45.43 vol. percent of thenaphtha charge stock, while decreasing the yield of raflinate from 28.07vol. percent to 19.46 vol. percent. The yield of benzene increased from3.50 vol. percent to 3.73 vol. percent for a net increase of 0.23 vol.percent, and the yield of toluene increased from 8.60 vol. percent to9.23 vol. percent for a net increase of 0.63 vol. percent. The yield ofmixed ethylbenzene and Xylenes increased from 13.65 vol. percent to17.34 vol. percent for a net increase of 3.69 vol. percent, while thecommercially less desirable aromatics containing nine or more carbonatoms per molecule increased from 15.10 vol. percent to 15.13 vol.percent for a net increase of only 0.03 vol. percent. The total aromaticyield was thus increased 4.58 vol. percent, while the yield ofparaifinic raflinate was decreased 8.61 vol. percent.

Additional advantages to the present invention may be summarized. Thusby fractionating the raflinate to provide the selected paraflinicraffinate fraction for recycle to the catalytic reformer, noaccumulation of hexanes and heptanes occurs within the process while thereforming catalyst is protected from an accelerated decline in activity.By sending the selected paraffinic raifinate to the last of the severalreforming reactors when the naphthene content of the selected raffinateis less than 10.0 vol. percent, or when the olefin content exceeds 1.0vol. percent, the reforming catalyst is most effectively used to balancethe desired chemical reactions and the catalyst is protected frompremature deactivation. In addition, by elimination of the recycledparamnic raifinate from the front of the reforming zone, the size of theprior heaters, reactors, and process lines may be reduced and therebythe capital and operating expenses are reduced. Since the selectedparaffiuic rafimate is obtained by fractionation to meet deslredspecifications, flexibility is inherent in the inventive process. Theoperation of the raflinate fractionation zone may be adjusted as marketsfor paraffinic rafiinate products vary, provided only that theparaffinic rafiinate fraction which is recycled to the catalyticreforming zone be comprised of hydrocarbons having at least eight carbonatoms per molecule and that this recycle stream has substantial freedomfrom polycyclic aromatics. Other advantages inherent to the inventiveprocess may be readily determined by those skilled in the art ofhydrocarbon processing.

Although the discussion of the present invention has been oriented tothe maximization of aromatic hydrocarbons as specific products, it mustbe realized that the present invention is not so limited. Since aromatichydrocarbons are high in octane, the inventive process is equally usefulin providing a means of producing high octane gasoline. Thus, thearomatics produced could be blended in whole or in part with any or allof the other liquid product streams leaving the process in anyproportions which may be required to result in a gasoline of the desiredquality. However, the manner in which the product streams leaving theinventive process are subsequently utilized has no bearing on thebroadness of the present invention.

I claim as my invention:

1. Process for the production of aromatic hydrocarbons which comprisesthe steps of:

(a) contacting a hydrocarbon feed stock containing naphthenic andparaffinic compounds with hydrogen in a reaction zone under conditionssuitable to convert at least a portion of said naphthenes into aromaticcompounds;

(b) separating the eflluent therefrom into a hydrogenrich gas productand a product containing said aromatic compounds;

(c) subjecting said aromatic-containing product to conditions sufiicientto produce a first paraflinic product containing polycyclic aromaticcompounds and a product comprising high-purity monocyclic aromatichydrocarbons;

(d) recovering said high-purity monocyclic aromatic product;

(e) separating said first parafiinic product into at least a secondparaflinic product comprising hydrocarbons having at least eight carbonatoms per molecule and having substantial freedom from said polycyclicaromatic compounds; and

(f) returning at least a portion of said second paraflinic product tosaid reaction zone wherein at least a portion of said product isconverted to aromatic compounds.

2. Process for the production of aromatic hydrocarbons which comprisesthe steps of (a) contacting a hydrocarbon feed stock containingnaphthenic and paraffinic compounds with hydrogen in a reaction zoneunder conditions suitable to convert at least a portion of saidnaphthenes into aromatic compounds;

( b) separating the effiuent therefrom into at least a hydrogen-rich gasproduct and a product containing said aromatic compounds;

(c) subjecting said aromatic-containing product to conditions sufficientto provide a light aromatic-containing fraction comprised ofhydrocarbons containing from about six to about eight carbon atoms permolecule and a heavy aromatic-containing fraction comprised ofhydrocarbon containing about nine or more carbon atoms per molecule;

((1) separating said light aromatic-containing fraction into a firstparaffinic fraction and a light high-purity monocyclic aromatic product;

(e) separating said heavy aromatic-containing fraction into a secondparaffinic fraction containing polycyclic aromatic compounds and a heavyhigh-purity monocyclic aromatic product;

(f) recovering said light monocyclic aromatic product and said heavymonocyclic aromatic product;

(g) subjecting said first paraffinic fraction and said second paraffinicfraction to conditions sufiicient to 15 provide a third paraffinicfraction comprising hydrocarbons having at least eight carbon atoms permolecule, and having substantial freedom from said polycyclic aromaticcompounds; and

(h) returning at least a portion of said third paraffinic fraction tosaid reaction zone wherein at least a portion of said fraction isconverted to aromatic compounds.

3. Process of claim 1 wherein said second paratfinic product has an endboiling point not greater than 350 F.

4. Process of claim 2 wherein said third paraffinic fraction has an endboiling point not greater than 350 F.

5. Process for the production of aromatic hydrocarbons which comprisesthe steps of:

(a) contacting a hydrocarbon feed stock containing naphthenic andparafiinic compounds with hydrogen in a reaction zone containing aseries of contact sections maintained under conditions suitable toconvert at least a portion of said naphthenes into aromatic compounds;

(b) separating the efiiuent therefrom into a hydrogenrich gas productand a product containing said aromatic compounds;

(c) subjecting said aromatic-containing product to conditions sufficientto produce a first paratfinic product containing polycyclic aromaticcompounds and a product comprising high-purity monocyclic aromatichydrocarbons;

(d) recovering said high-purity monocyclic aromatic product;

(e) separating said first paraffinic product into at least a secondparafiinic product comprising hydrocarbons having at least eight carbonatoms per molecule and having substantial freedom from said polycyclicaromatic compounds; and

(f) returning at least a portion of said second paraffinic product tothe last of said contact sections wherein at least a portion of saidproduct is converted to aromatic compounds.

6. The process of claim 5 wherein said second paraffinic product has anend boiling point not greater than about 350 F.

7. Process for the production of aromatic hydrocarbons which comprisesthe steps of:

(a) contacting a hydrocarbon feed stock containing 16 naphthenic andparafiinic compounds with hydrogen in a reaction zone containing aseries of contact sections maintained under conditions suitable toconvert at least a portion of said naphthenes into aromatic compounds;

(b) separating the eflluent therefrom into at least a hydrogen-rich gasproduct and a product containing said aromatic compounds;

(c) subjecting said aromatic-containing product to conditions sufiicientto provide a light aromaticcontaining fraction comprised of hydrocarbonscontaining from about six to about eight carbon atoms per molecule and aheavy aromatic-containing fraction comprised of hydrocarbons containingabout nine or more carbon atoms per molecule;

(d) separating said light aromatic containing fraction into a firstparaffinic fraction and a light highpurity aromatic product;

(e) separating said heavy aromatic-containing fraction into a secondparafiinic fraction containing polycyclic aromatic compounds and a heavyhigh-purity monocyclic aromatic product;

(f) recovering said light monocyclic aromatic product and said heavymonocyclic aromatic product;

g) subjecting said first paraffinic fraction and said second parafiinicfraction to conditions sufficient to provide a third paraflinic fractioncomprising hydrocarbons having at least eight carbon atoms per molecule,and having substantial freedom from polycyclic aromatic compounds; and

(h) returning at least a portion of said third paraffinic fraction tothe last of said series of contact sections wherein at least a portionof said fraction is converted to aromatic compounds.

8. The process of claim 7 wherein said third paraffinic fraction has anend boiling point not greater than about 350 F.

References Cited UNITED STATES PATENTS 2,870,226 1/1959 Deanesly 260-6682,909,477 10/1959 Muller 20865 2,915,455 12/1959 Donaldson 208-65ABRAHAM RIMENS, Primary Examiner.

